Wireless communication systems currently in practical use can be broadly divided into two groups. One group comprises cellular wireless network systems (hereinafter referred to as “cellular systems”) typified by GSM (Global System for Mobile Communications) and PDC (Personal Digital Cellular), and the other comprising wireless local area network systems (hereinafter referred to as “wireless LAN systems”) typified by IEEE802.11a/b and HYPERLAN2.
In a cellular system, since mobile terminals have mobility, there are excellent management functions for related mobile terminal location information, and also excellent authentication functions necessary when a message service or encryption is implemented. In addition, this kind of system can be used across a wide range, and is effective as a voice communication system.
In a wireless LAN system, on the other hand, large-capacity data transmission can be achieved, with maximum data transmission capacities of 11 Mbps with IEEE802.11b, and 54 Mbps with IEEE802.11a and HYPERLAN2.
Also, data transmission systems that combine the above-described advantages of cellular systems and wireless LAN systems and avoid their shortcomings have been studied (for example, Unexamined Japanese Patent Publication No. HEI 9-130405 (pages 7-8, FIG. 1)).
However, in a cellular system, when a large number of users are in a communicating state and communication density is high, capacity problems occur even in the present situation, and there is also a problem of not being able to provide sufficient data transmission capacity for large-capacity data transmission expected henceforth.
With a wireless LAN system, on the other hand, there is a problem of inadequacy of mobile terminal location information management functions as provided in a cellular system.
Also, simple authentication between an access point and mobile terminal such as ESS-ID (Extended Service Set Identity) is used for authentication performed when a link is established with a mobile terminal, and encryption technology for improving wireless LAN security, such as the WEP (wired equivalent privacy) security specification supported by IEEE802.11, for example, is used.
With such simple authentication and WEP encryption technology, a key can easily be deciphered by deciphering and stealing secret key data and a MAC (Media Access Control) address from a received wireless signal. Therefore, bugging, masquerading, and suchlike activities are possible, and vulnerability in terms of security is demonstrated.